Mechanical structures having insulated parts and method of making same



Get. 18, 1955 KURATH 2,721,283

MECHANICAL STRUCTURES HAVING INSULATED IN V EN TOR. 270/27 ffu/azfz, BY

Oct. 18. 1955 F. KURATH 2,721,283

MECHANICAL STRUCTURES HAVING INSULATED PARTS AND METHOD OF MAKING SAME Filed March 22, 1952 2 Sheets-Sheet 2 IN V EN TOR.

flary/[umZ/z, BY n lwfimp Unite States Patent SAME Franz Kurath, Tucson, Ariz.; Marie A. Kurath, executrix of the estate of said Franz Kurath, deceased Application March 22, 1952, Serial No. 278,097

4 Claims. (Cl. 310235) This invention relates to a new and improved method of mechanically attaching independent elements or parts of mechanical structures, such as associated metallic parts, and at the same time providing an excellent insulation therebetween.

This invention also relates to new and improved structures resulting from the practice of this process.

Although the invention is not to be limited in its application to the production of commutators for electric motors, it is particularly adapted for such use. Accordingly, it is here illustrated as applied to the manufacture of commutators of the type which are now formed by assembling individual segments of copper into a ring or annulus, and in which each copper segment is separated and electrically insulated from the adjacent segment by suitable insulation.

It is common today to form such commutators by utilizing insulation cut or punched from sheet stock formed as to size and shape to the contour of the copper segments, and to insert such insulating sheets between the adjacent faces of each of the copper segments, respectively. It is also common to assemble the associated and insulated copper segments in a retaining ring and to introduce in the center thereof a metal hub which in turn is electrically insulated from the annular surface provided by the ends of the copper segments, respectively.

The present invention contemplates the association of metal parts such as the copper segments and the steel hub of commutators of the type referred to, which are so formed as to provide surfaces capable of establishing a mechanical interlock when certain of the opposed surfaces of the associated parts are pressed away from each other, as, for instance, by means of the expansion of an intermediate material. For instance, as applied to the construction of commutators of the type above referred to, interlocking surfaces may be produced on the segments, respectively, and the steel hub, and such surfaces may be formed as keystone projections and associated recesses, with suitable space therebetween to accommodate an intermediate filling material.

lnstead of the mica or other insulating inserts now used in the art, the present invention contemplates the use of a filler consisting of magnesium hydroxide formed in situ from electrically fused magnesium oxide and water, the latter being preferably provided in the form of steam under the action of heat. in practice, the space between the interlocking surfaces is first filled with the magnesium oxide (MgO), and thereafter the magnesium oxide is subjected to the action of water supplied in the form of steam. The MgO plus H20 yields Mg(OH)2, changing the specific gravity of the material from 3.7 to 2.38 and at the same time undergoing a physical change from a solid, fused kernal to an extremely fine, amorphous powder. The combined chemical and physical change brings about a compacting of the insulation more than sufiicient to hoid the parts in mechanical assembly to form a rigid structure capable of withstanding all conditions encountered in normal operation. At the same time, the

Mg(OH)2 provides an electrical insulation of high order which is completely inorganic and which, when employed in the construction of commutators or the like, will successfully withstand temperatures higher than those which have been successfully withstood in the past.

In practice, there is no actual bonding between the magnesium hydroxide and the mechanically interlocked parts, but due to the mechanical arrangement, wherein a keystone opening in one of the parts and a keystone projection on the other of the parts are provided, the wedging and locking action produced by the expanded magnesium hydroxide results in a firm mechanical attachment of the parts in proper relationship.

As one specific embodiment of the invention, reference may be had to the accompanying drawing, which illustrates the construction and method of forming a commutator of the type above referred to, and in which Figure 1 represents a plan view of a series of copper segments and a fixture ring in associated relationship adapting the same to be formed into a commutator.

Figure 2 is a cross-sectional view taken on the line 22 of Figure 1.

Figure 3 is a side elevational view similar to Figure 2 but showing in addition thereto the associated steel hub and center member of the positioning fixtures; and

Figure 4 illustrates the positioning fixture complete with the hub and the segments in assembled relation, with the magnesium oxide filling the space therebetween.

The assembly shown in Figure 3 is complete except for the closing member, and in the form shown is ready to receive the magnesium oxide in the space between the segments and the hub and in the spaces between the segments themselves. The assembly as shown in Figure 4 is ready for the steam treatment.

Reference to the drawing will show that the commutator is made up of a plurality of segments 10, arranged in annular relation with a space 11 between each segment. In this instance, twelve segments are shown, each of which is equally spaced from the other, and all of which are held in proper relation within the fixture ring 12. The fixture ring is preferably provided with splines 13 extending radially inwardly from its inner face, as best shown in Figures 2 and 3. These splines serve accurately to space each segment from its adjacent segments. As shown in Figure 2, each spline terminates short of the top and bottom surfaces of the fixture ring so as not to interfere with the reception of the top and bottom portions of the positioning fixture to be subsequently associated therewith.

As shown in Figures 3 and 4, the commutator also ineludes in its construction a hub 14 which has an annular enlargement 15 at the base thereof and a threaded portion 16 at the top. The enlarged member 17 has screwthreaded engagement with the threads 16 at the top to form a removable counterpart to the enlargement 15 located at the bottom. The enlargement 15 and the removable portion 17 have inclined faces of such construction as to form an annular recess in the hub, having a cross-sectional shape resembling that of a keystone. This hub member is adapted to be assembled on the center post 18 of the bottom member 18 of the positioning fixture in the manner illustrated in Figure 3.

It will be noted that the outer edge of the member 18 is provided with an enlarged, upstanding, annular portion which fits into the recess 19 provided by the lower ends of the segments, respectively, and the lower edges of the intermediate splines 13 on the inner surface of the fixture ring. The space between the annular enlargement 19 and the upstanding portion of the positioning fixture is formed to fit the lower portion 15 of the hub so that when the parts thus described have been assembled, as illustrated in Figure 3, the keystone projections of the segments,

be threadedly placed on the upper end of the hub in the manner illustrated in Figure 3.

With the parts thus assembled, the positioning fixture can be mounted on a vibrating device and, while being vibrated, electrically fused magnesia (MgO) is introduced in the upper annular space 26 occurring between the upper portion of the fixture ring and the removable member 17 of the hub. The quantity introduced is preferably carefully measured and of predetermined mesh so that under the vibrating action the space between the copper seg ments and the hub and the spaces between the copper segments are completely filled. Thereafter, the upper cap member 21, shaped in the manner illustrated in Figure 4, is placed on top of the positioning fixture and held in place by the center bolt 22 which has screw-threaded engagement as at 23 with the upstanding portion 18 of the positioning fixture. The cap has an annular enlargement, as illustrated, which exactly fills the annular space between the upper portion of the fixture ring 12 and the removable member 17 of the hub.

Furthermore, spaced annularry around the cap are a plurality of openings 24-44 which admit steam into the hub openings 25-25, which in turn lead into the space between the segments and the hub. With the cap member thus tightly held in position, the entire assembly as shown in Figure 4, with the fused MgO confined in the spaces provided therefor, is next exposed to the action of steam by placing the fixture in a suitable pressure vessel or autoclave. Under the action of the steam, which enters through the openings 24 and 25, the MgO undergoes a chemical change forming the Mg(OH)z, and in consequence the specific gravity of the material is changed from 3.7 to 2.38, and at the same time the physical form is altered from a solid fused kernal to an extremely fine amorphous powder. The combined chemical and physical changes bring about a compacting of the insulation more than suificient to hold the commutator parts in assembled relation after their removal from the fixture or mold. The assembly is rigidly formed and permanently maintained under all conditions encountered in normal use. In addition, the Mg(OH)2 formed in the space between the segments and the segments and the hub provides electrical insulation of excellent quality which, due to the fact that it is inorganic, will withstand temperatures higher than those which can be withstood with insulating materials now in use.

It is to be understood that although the invention as illustrated is applied to commutators, the invention is to be considered sufficiently broad to embrace other constructions and to include mechanical interlocking of parts or elements of a structure by forming in situ expanded magnesium hydroxide in the space between adjacent faces of a cooperating interlocking projection and recess formed, respectively, thereon.

What is claimed is:

l. The method of mechanically attaching independent elements to form a united structure, which comprises forming a part of one of said elements and a cooperating recess in the other of said elements, in such manner that said part fits into said recess with each presenting an opposed but spaced face to the other, inserting fused magnesium oxide capable of expanding on subsequent treatment in said space, and then subjecting the same to treatment causing such expansion and thereby locking said elements in tight mechanical attachment.

2. The process of claim 1, further characterized in that said expansible substance is electrically fused magnesium oxide, and said expansion is effected by the step of exposing said magnesium oxide when in said space to the action of steam to form magnesium hydroxide in situ therein.

3. A unitary structure composed of independent elements, one of which has a projection thereon and another of which has a recess therein, said projection being disposed in said recess, and both being constructed to present opposed locking faces disposed in spaced relation to each other, said unitary structure having fused magnesium oxide in the space between said faces expanded in situ to provide a tight interlock between said elements.

4. The unitary structure defined in claim 3, further characterized in that said elements comprise a plurality of segments and a hub of a commutator, and in which the segments are mechanically locked to said hub and insulated therefrom and from each other by the magnesium oxide expanded in situ in said space by the action of steam.

References Cited in the file of this patent UNITED STATES PATENTS 1,287,309 Hensley Dec. 10, 1918 1,572,714 Frosell Feb. 9, 1926 1,778,992 Wulfert Oct. 21, 1930 1,845,114 Apple Feb. 16, 1932 OTHER REFERENCES Smooth-On Handbook, 20th edition, published by Smooth-On Manufacturing Co., 570 Communipaw Ave, Jersey City, N. 1., 1924, pages 18, 19, 22.

Girardot abstract 160, 516, published August 5, 1952. 

